Typically, a code division multiple access (CDMA) transmission scheme for use in a universal mobile telecommunication system (UMTS) acting as a third-generation wireless communication system has difficulty in processing large amounts of wireless data, such that many developers are conducting intensive research into an orthogonal frequency division multiplexing (OFDM) transmission scheme acting as a fourth-generation wireless communication system. The OFDM transmission scheme is also applied to an Evolved-Universal Mobile Telecommunications System (E-UMTS) acting as a fourth-generation mobile communication system based on the above UMTS.
FIG. 1 is a structural diagram illustrating a network structure of the E-UMTS acting as a fourth-generation mobile communication system. The E-UMTS system is developed from a conventional Wideband Code Division Multiple Access (WCDMA) UMTS system as previously stated above, and conducts intensive research into a basic standardization process in the current 3rd Generation Partnership Project (3GPP). The E-UMTS system may also be called a Long Term Evolution (LTE) system. Detailed descriptions of technical specifications of the UMTS or E-UMTS have been prescribed in Releases 7 and 8 of Technical Specification Group Radio Access Network of the 3rd Generation Partnership Project (GPP).
Referring to FIG. 1, an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) includes a plurality of eNode-Bs (also called eNBs). The eNode-Bs (eNBs) are connected to each other via an X2 interface. Each eNB is connected to a user equipment (UE) via a wireless interface, and is connected to an Evolved Packet Core (EPC) via an S1 interface.
The E-UMTS system uses an orthogonal frequency division multiplexing (OFDM) scheme in a downlink, and uses a Single Carrier-Frequency Division Multiple Access (SC-FDMA) scheme in an uplink. The OFDM system acting as a multi-carrier scheme allocates resources on the basis of a plurality of subcarriers grouping some carriers, and uses an Orthogonal Frequency Division Multiple Access (OFDMA) scheme as an access scheme.
Active carriers for use in a physical layer of the OFDM or OFDMA system are divided into a plurality of groups, such that the divided active carriers are transmitted to different reception ends of individual groups. Radio resources allocated to individual UEs are defined by a two-dimensional (2D) time-frequency region (also called a 2D time-frequency domain), and are considered to be a set of consecutive subcarriers. A single time-frequency domain of the OFDM or OFDMA system is denoted by a rectangle decided by time coordinates and subcarrier coordinates. In other words, a single time-frequency domain can be denoted by a rectangle defined by both a symbol of at least one time axis and a sub-carrier of several frequency axes.
The time-frequency domain may be allocated to an uplink of a specific user equipment (UE). In a downlink, an eNode-B may transmit the time-frequency domain to a specific UE. In order to define the above-mentioned time-frequency domain in a two-dimensional (2D) space, a predetermined number of OFDM symbols must be provided to the time domain, and a predetermined number of consecutive subcarriers must be provided to the frequency domain such that the consecutive subcarriers will begin at a predetermined position which is spaced apart from a reference point of the frequency domain by a predetermined offset.
In the Evolved Universal Mobile Telecommunications System (E-UMTS) system being intensively researched by many developers, radio frames of 10 ms have been used, and a single radio frame includes 10 subframes. In other words, a single subframe corresponds to the duration of 1 ms. A single resource block includes a single subframe and 12 subcarriers. Each of the 12 subcarriers includes a band of 15 kHz. A single subframe includes several OFDM symbols. Some parts (e.g., a first symbol) of the several OFDM symbols may be used to transmit L1/L2 control information.
FIG. 2 is a conceptual diagram illustrating a physical channel structure for use in the E-UMTS system. Referring to FIG. 2, a single sub-frame includes a hatched part serving as an L1/L2 control information transmission part and a non-hatched part serving as a data transmission area.
Radio interface protocol layers between the UE and the network including the eNode-B are classified into a first layer (L1), a second layer (L2), and a third layer (L3) on the basis of three lower layers of an Open System Interconnection (OSI) reference model well known to a communication system field. The first layer (L1) provides an information transfer service using a physical channel. A radio resource control (RRC) layer located at the third layer (L3) controls radio resources between the UE and the network. For this operation, the RRC layer exchanges the RRC message between the UE and the network. The RRC layer may be distributed to network nodes (e.g., eNode-B and AG), or may also be located independent of the eNode-B or the AG.
FIG. 3 is a conceptual diagram illustrating an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). In FIG. 3, a hatched part shows functional entities of a user plane, and a non-hatched part shows functional entities of a control plane.
FIGS. 4A and 4B show a radio interface protocol structure between the UE and the E-UTRAN. FIG. 4A shows a control plane protocol structure, and FIG. 4B shows a user plane protocol structure.
Referring to FIGS. 4A and 4B, a radio interface protocol includes a physical layer, a data link layer, and a network layer in a horizontal direction. In a vertical direction, the radio interface protocol includes a user plane for transmitting data information and a control plane for transmitting control signals (i.e., signaling messages). The protocol layers shown in FIGS. 4A and 4B can be classified into a first layer (L1), a second layer (L2), and a third layer (L3) on the basis of three lower layers of an Open System Interconnection (OSI) reference model well known to a communication system field.
A physical layer serving as the first layer (L1) transmits an information transfer service to an upper layer over a physical channel. The physical layer is connected to a Medium Access Control (MAC) layer serving as an upper layer over a transport channel. Data is transferred from the MAC layer to the physical layer over the transport channel, or is also transferred from the physical layer to the MAC layer over the transport channel. Data is transferred among different physical layers over the physical channel. In other words, data is transferred from a transmitting physical layer to a receiving physical layer over the physical channel. In the case of the E-UMTS system, the above-mentioned physical channel is modulated according to an orthogonal frequency division multiplexing (OFDM) scheme, so that the E-UMTS system uses time and frequency information as radio resources.
The MAC layer of the second layer (L2) transmits services to a Radio Link Control (RLC) layer serving as an upper layer over a logical channel. The Radio Link Control (RLC) layer of the second layer (L2) supports transmission of reliable data. A PDCP layer of the second layer (L2) performs header compression to reduce an amount of unnecessary control information, such that transmission (Tx) data of IP packets (e.g., IPv4 or IPv6 packets) can be effectively transmitted in a relatively narrow-bandwidth air space.
The radio resource control (RRC) layer located at the bottom of the third layer (L3) is defined on a control plane only. In association with configuration, re-configuration, and release of radio bearers (RBs), the RRC layer controls the logical channels, the transport channels, and the physical channels. In this case, the above radio bearer (RB) is provided from the second layer (L2) to perform data communication between the UE and the UTRAN.
The OFDM-based wireless communication scheme uses a variety of downlink transport channels for transmitting data from the eNode-B to the UE, for example, a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting paging messages, and a downlink shared channel (DL-SCH) for transmitting user traffic or control messages. Traffic or control messages of a downlink multicast or a broadcast service may be transmitted over a downlink SCH (DL-SCH), or may also be transmitted over an additional downlink multicast channel (MCH). In the meantime, there are a variety of uplink transport channels for transmitting data from the UE to the network, for example, a random access channel (RACH) for transmitting initial control messages, and an uplink shared channel (UL-SCH) for transmitting user traffic or control messages.
A variety of logical channels located on the transport channels are mapped to the transport channels. For example, the logical channels may be a broadcast channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic channel (MTCH).
In order to transmit most signals except for either specific control signals or specific service data, the eNode-B and the UE use the DL-SCH as a transport channel. The eNode-B and the UE transmit and receive data over a Physical Downlink Shared Channel (PDSCH) to which the DL-SCH is allocated. Also, information indicating which one of UEs (one or more UEs) will receive PDSCH data, the other information indicating how to receive PDSCH data in the above UEs or how to decode the PDSCH data may be transmitted over a Physical Downlink Control Channel (PDCCH). The PDCCH transmits transport formats associated with the DL-SCH and PCH, resource allocation information, and hybrid ARQ information.
During a connection time between the UE and the E-UTRAN, in association with a specific PDCCH which is CRC-masked with a Radio Network Temporary Identity (RNTI), if one or two more UEs contained in a cell receiving the specific PDCCH determine the presence of another PDCCH masked with the same RNTI as those of the above UEs, the one or two more UEs receive their associated PDSCH via the received PDCCH information.
FIG. 5 shows exemplary methods for transmitting data from an eNode-B (eNB) to a user equipment (UE). Referring to FIG. 5, if the UE receives specific data from the eNode-B (eNB) over a data channel such as PDSCH, the eNB can transmit specific data for a predetermined period of time to reduce an amount of power consumption, or can also transmit the specific data after the lapse of a specific time interval after a certain event has occurred. Therefore, the UE has only to receive data from the eNB during the above specific time only, such that it is able to reduce an amount of power consumption in the remaining times other than the above specific time.
However, the above specific data may have different amounts of information (i.e., different numbers of bits) according to various situations. Also, a Long Term Evolution (LTE) system supporting large amounts of wireless data basically considers a dynamic scheduling scheme, such that the number of bits contained in transmittable information is also dynamically changed to another according to a current channel situation. In other words, the amount of requested radio resources may be changed whenever the above-mentioned specific data is transmitted. For example, in order to transmit the above-mentioned specific data, 5 subframes or 10 subframes may be needed.
Provided that the above specific data is transmitted for successive Transmission Timing Interval (TTIs) and 5 TTIs are requested for a current situation, the eNB transmits the specific data associated with the above UE during the 5 TTIs. For the convenience of description, the following description assumes that the above-mentioned Transmission Timing Interval (TTI) corresponds to the length of a single subframe. However, the UE is unable to determine how many TTIs are needed to receive the specific data from the eNB. As a result, the UE attempts to receive the specific data from the eNB during even a sixth TTI. If the UE does not receive PDCCH or PDSCH data during a corresponding TTI, it is able to decide that the above specific data has been completely received. However, the UE has attempted to receive data of the sixth TTI having no need to be received, resulting unnecessary power consumption occurs in the UE.
In order to allow the UE to receive data, the UE defines a time window (also called a window interval), such that the UE may attempt to receive messages in only the time window. The UE receives information of the window interval from system information. Accordingly, when the UE receives data, it receives the data during a reception (Rx) interval (e.g., 8 TTIs) acting as the window interval. However, in case of using the time window, many more intervals than the requested TTIs must be established due to the above scheduling problem, such that the UE unnecessarily attempts to receive messages, resulting in the occurrence of unnecessary power consumption. For example, although a window value is set to 10 TTIs, the UE completely receives data during 5 TTIs, and then continuously attempts to receive messages during the remaining 5 TTIs other than the above 5 TTIs, resulting in the occurrence of UE's power consumption.
FIG. 6 shows that a transmission interval of specific data is extended due to transmission of higher priority data. If data is transmitted according to eNB's scheduling situations in which transmission environments and radio-resource conditions are reflected, the data may not be transmitted during successive TTIs. As shown in FIG. 6, if 5 TTIs are needed to transmit data from the eNB to an arbitrary UE, transmission of data having priority higher than that of the above data occurs in an (N+2)-th TTI although the eNB actually desires to transmit the above data in the range from an N-th TTI to an (N+4)-th TTI, the eNB may not transmit the above specific data in the (N+2)-th TTI. As a result, the transmission interval of the above data is extended from the N-th TTI to an (N+5)-th TTI. In this case, although the UE is able to receive data using the above-mentioned reception (Rx) method, it should be noted that it may receive unnecessary data as necessary.
In the meantime, a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) are adapted to transmit paging-associated control information and paging messages. A method for paging at least one UE from the eNB will hereinafter be described in detail.
The term “Paging” is a specific behavior that an eNB searches for one or more UEs to achieve certain purposes. In other words, the term “paging” is a specific function that the eNB pages one or more UEs. This paging function allows the eNB to search for a desired UE from among several UEs, and allows the UE not to be awakened, such that a UE's power-saving consumption results in the implementation of UE's power-saving effect. In other words, the UE is usually in a sleeping mode (also called a sleep mode), but is then woken up upon receiving a paging signal from the eNB such that it conducts commands requested by the eNB.
In order to allow the sleep-mode UE to recognize the above paging signal from the eNB, the sleep-mode UE must be periodically woken up to check the presence or absence of paging information received in the UE itself. The above-mentioned UE's periodic wake-up operation is called a discontinuous reception (DRX), and the LTE system uses this DRX method as a method for receiving UE's paging information.
FIG. 7 shows a variety of paging periods for use in the paging process according to the conventional art. A process for transmitting a paging channel from an eNode-B (eNB) to one or more UEs according to the conventional art is as follows. First, if the UE is registered in the eNB under an idle mode, a paging group is allocated to the UE. The paging group includes a paging indicator (PI). In more detail, if a paging message toward any UE contained in the paging group occurs, the paging indicator (PI) periodically appears in a paging-indication channel. If a specific UE of a CELL_PCH mode from among several connected modes receives the PI, then the specific UE determines the presence or absence of a paging message associated with the specific UE itself.
Under the CELL_PCH mode, the UE can conduct the above-mentioned discontinuous reception to reduce an amount of UE's power consumption. Thus, the eNode-B (eNB) constructs a plurality of paging occasions at intervals of a predetermined time called a paging interval, a specific UE receives only a specific paging occasion selected from among all paging occasions, such that it can acquire a paging message. The above specific UE does not receive data of the paging channel in the remaining paging occasions other than the above-mentioned specific paging occasion. Generally, the paging occasion corresponds to a time interval during which data is transmitted from a Medium Access Control (MAC) end of a wireless protocol structure to a physical end. In case of a UMTS or E-UMTS system, the paging occasion corresponds to a Transmit Time Interval (TTI).
The eNB and the UE indicates whether the paging message appears using a paging indicator (PI) as a specific value for indicating transmission of the paging message. The UMTS system allocates a single bit (i.e., 1 bit) to indicate the PI, such that it indicates whether the paging message appears using the 1 bit. The E-UMTS (Evolved Universal Mobile Telecommunications System) defines a specific identity (e.g., a Paging Indicator-RNTI (PI-RNTI)) to indicate the PI, such that the network is able to inform the UE of paging-information transmission. For example, the UE is woken up at intervals of a discontinuous reception (DRX) period, and receives control information for indicating whether the paging message appears or not. If the received control information includes the PI such as a PI-RNTI, the above UE receives a channel including the above control information and its associated paging message, recovers the received channel, and determines whether its own identifier (i.e., UE identity) exists in the above paging message. If the above paging message includes a UE's identity such as an International Mobile Station Identity (IMSI), the UE answers the network to conduct RRC connection, and then receives a desired service. Also, each paging message may include information of a paging cause to indicate the paging cause. As a result, the individual paging messages can indicate a variety of calling contents, for example, a conversational call, a streaming call, an interactive call, a background call, a high-priority signaling call, and a low-priority signaling call.
As described above, the above-mentioned conventional art does not include specific information indicating whether data to be received in the UE is the last data, such that the UE must attempt to receive unnecessary data, resulting in the occurrence of a large amount of unnecessary power consumption. A paging message for paging a single UE includes the paging-cause information and the UE identity. Thus, if several UEs are simultaneously paged (or simultaneously called) when a cell providing a narrow bandwidth transmits the paging message, the paging message cannot be transmitted during a single paging occasion. So, this paging message can be transmitted after the lapse of the next paging period, resulting in the occurrence of an unexpected paging delay.